The transmission of light through thin fibers of glass or plastics has resulted in a variety of instruments for the visualization of otherwise inaccessible organs and tissues inside the human body. Such instruments are broadly referred to as endoscopes and have been useful in the diagnosis and treatment of, for example, gastro intestinal and respiratory diseases.
Fiberoptic endoscopes were first introduced about thirty years ago. Although they have gained wide acceptance where flexibility is required, medical personnel still prefer to use rod lenses or other alternatives. The reason being that they are annoyed by the fixed mosaic structure of a fiberoptic image. Also in most applications, the resolution of present fiberoptic endoscopes is generally inferior to other alternatives.
It is known in the art to scan with fiberoptics. If a multifiber is rotated, a concentric noise pattern is superimposed on the image. If the multifiber is not moved, a mosaic-like noise pattern is superimposed on the image.
In my parent application, a multifiber endoscope was disclosed with much improved resolution for a given diameter and which partially eliminated the fixed pattern noise typical of fiber endoscopes. However, I have found that even with rotational scanning there is still a residual fixed pattern streakiness comprising concentric circles even though the individual fibers themselves are no longer visible. Also, a small area near the axis of rotation has a very pronounced fixed pattern noise.
My present invention embodies a multiple-scanning technique for a multifiber which substantially reduces or eliminates the noise inherent in prior art multifiber endoscopes. The multiple scanning may comprise either a rotary and a chromatic scan or two rotary scans. In principle, many scanning combinations are possible but some scanning motions are difficult to achieve in a thin needle inserted into the body.
Rotary scan is particularly easy to achieve because the scanning motion at the distal end of the multifiber is driven by the torsion of the thin member itself and synchronism between the scan at the proximal and distal ends is almost guaranteed. Even a double rotary scan can be achieved. One example is a small eccentric rotation at one speed around a first axis superimposed over rotation at another speed around a second axis. That is, there is one rotation about a first axis and then rotation about another axis slightly displaced from the first axis and at, for example, one-tenth or ten times the angular velocity. To accomplish this, the fiber structure may rotate in a sleeve which has an eccentric bore which rotates in another sleeve.
In a preferred embodiment, the multiple scanning is achieved by using a rotary scan in combination with a prism and/or grating to provide a chromatic scan. The field of view is tipped and rotated. This chromatic scan can be accomplished by attaching a prism or blazed grating to the sleeve in which the fiber rotates and then rotating the sleeve so the image is scanned in a rotational pattern on the face of the fiber while the fiber rotates. The prism, at the distal end, spreads an image point into a linear rainbow and creates the equivalent of a linear scan. A prism at the proximal end rectifies the image back from a rainbow to a point. In transit, each original point travels through many fibers along the length of the rainbow. The final result is much the same as if there were a linear scan in the plane of the tipped axis. Even if the prism is not rotated, only the fiber itself being rotated, two scans have been accomplished--a rotary scan and the linear chromatic scan. This chromatic scan per se has been known to the art for several years and it leaves linear streakiness. The combination of the two scans gives a much improved appearance.
If the prism rotates with the fiber, there is still a rotational and chromatic scan. If the prism rotates at a different angular velocity (from the fiber), there is actually a triple scan--one linear chromatic scan and two rotational scans.
The tip angle provides for flexibility in the field angle if that is desired. Gratings also tip the field angle and give much greater dispersion than the prism and can also be used for chromatic scanning. Because the grating dispersion and prism dispersion are of opposite effects, it is possible to combine a prism and a grating to get no tip and a lot of dispersion or a lot of tip and a little dispersion or any combination therebetween.
In one aspect of the invention, the optics can look straight ahead with no increase in the field of view and not rotate the prism/grating but rotate the fiber and get a combination of chromatic and rotational scan.
In another aspect of the invention, the field angle can be tipped and the prism/grating not rotated (not expand the field of view but only tip it) to get a combination of rotary scan and chromatic scan.
In another aspect of the invention, in addition to the rotary scan of the multifiber, a prism/grating can be rotated to expand the field angle and have a double scan, if the prism and fiber are synchronized, or a triple scan, if they are not synchronized. In all embodiments, there is a proximal set of lenses, prism/grating conjugate to the distal optics to produce a still image.